Bidentate Interaction Research Articles

In situ infrared spectroscopic analysis of the adsorption of aromatic carboxylic acids to TiO 2, ZrO 2, Al 2O 3, and Ta 2O 5 from aqueous solutions

In situ infrared spectroscopy has been used to investigate the adsorption of a range of simple aromatic carboxylic acids from aqueous solution to metal oxides. Thin films of TiO 2, ZrO 2, Al 2O 3 and Ta 2O 5 were prepared by evaporation of aqueous sols on single reflection ZnSe prisms. Benzoic acid adsorbed very strongly to ZrO 2, in a bridging bidentate fashion, but showed only weak adsorption to TiO 2 and Ta 2O 5. Substituted aromatic carboxylic acids; salicylic, phthalic and thiosalicylic, were found to adsorb to each metal oxide. Salicylic and phthalic acids adsorbed to the metal oxides via bidentate interactions, involving coordination through both carboxylate and substituent groups. Thiosalicylic acid adsorbed to the metal oxides as a bridging bidentate carboxylate with no coordination through the thiol substituent group.

Metal salts interaction with acrylic acid-maleic acid copolymer: An infrared spectroscopic study

A study was carried out in which aqueous solutions of acrylic acid–maleic acid copolymer (mole ratio of monomers: 3:2) were diluted with solutions of various salts [NaCl, MgCl2, CaCl2, SrCl2, ZnCl2, Al(NO3)3 and Fe(NO3)3]. This copolymer was found to interact with all these salts to make solutions of enhanced acidity that infrared spectroscopy suggested was a result of charge stabilization of the polyanion by counterions occupying atmospheric or site-bound locations. The cations of the salts NaCl, MgCl2, CaCl2 and SrCl2 appeared to occupy atmospheric positions only; in contrast, with poly(acrylic acid) they showed some site binding. Zinc ions, on the other hand, gave identical bridging bidentate interactions with both polymers. The cations from the trivalent salts Al(NO3)3 and Fe(NO3)3 were atmospheric and site bound (bridging bidentate), respectively, and these were also different from their interactions with poly(acrylic acid). The addition of Fe(NO3)3 to the copolymer caused gelation, as with poly(acrylic acid), but formation of the gel was slower and did not result in phase separation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1680–1684, 2000

Protein-carbohydrate interactions defining substrate specificity in Bacillus 1,3-1,4-beta-D-glucan 4-glucanohydrolases as dissected by mutational analysis.

The carbohydrate-binding site of Bacillus macerans 1,3-1, 4-beta-D-glucan 4-glucanohydrolase has been analyzed through a mutational analysis to probe the role of protein-carbohydrate interactions defining substrate specificity. Amino acid residues involved in substrate binding were proposed on the basis of a modeled enzyme-substrate complex [Hahn, M., Keitel, T., and Heinemann, U. (1995) Eur. J. Biochem. 232, 849-859]. The effects of the mutations at 15 selected residues on catalysis and binding were determined by steady-state kinetics using a series of chromogenic substrates of different degree of polymerization to assign the individual H-bond and hydrophobic contributions to individual subsites in the binding site cleft. The glucopyranose rings at subsites -III and -II are tightly bound by a number of H-bond interactions to Glu61, Asn24, Tyr92, and Asn180. From k(cat)/K(M) values, single H-bonds account for 1.8-2.2 kcal mol(-)(1) transition-state (TS) stabilization, and a charged H-bond contributes up to 3.5 kcal mol(-)(1). Glu61 forms a bidentated H-bond in subsites -III and -II, and provides up to 6.5 kcal mol(-)(1) TS stabilization. With a disaccharide substrate that fills subsites -I and -II, activation kinetics were observed for the wild-type and mutant enzymes except for mutations on Glu61, pointing to an important role of the bidentate interaction of Glu61 in two subsites. Whereas removal of the hydroxyl group of Tyr121, initially proposed to hydrogen-bond with the 2OH of Glcp-I, has essentially no effect (Y121F mutant), side-chain removal (Y121A mutant) gave a 100-fold reduction in k(cat)/K(M) and a 10-fold lower K(I) value with a competitive inhibitor. In subsite -IV, only a stacking interaction with Tyr22 (0.7 kcal mol(-)(1) TS stabilization) is observed.

In situ infrared spectroscopic analysis of the adsorption of aliphatic carboxylic acids to TiO 2, ZrO 2, Al 2O 3, and Ta 2O 5 from aqueous solutions

The adsorption of a range of aliphatic mono- and di-carboxylic acids to metal oxides has been investigated using in situ attenuated total reflectance infrared spectroscopy. Thin films of TiO 2, ZrO 2, Al 2O 3, and Ta 2O 5 were prepared by evaporation the aqueous colloid oxides on single reflection ZnSe prisms. Formic and acetic acids were found to bind to ZrO 2 and Ta 2O 5, but showed no adsorption to TiO 2 and Al 2O 3. The dicarboxylic acids, oxalic, malonic, succinic, adipic, maleic, and fumaric acids, were found to adsorb to each of the metal oxide substrates. Oxalic and malonic acids were coordinated via ester linkages involving both carboxylate groups. The longer chain dicarboxylic acids coordinated via bridging bidentate interactions through each carboxylate group.

The R78K and D117E active-site variants of Saccharomyces cerevisiae soluble inorganic pyrophosphatase: structural studies and mechanistic implications

We have solved the structure of two active-site variants of soluble inorganic pyrophosphatases (PPase), R78K and D117K, at resolutions of 1.85 and 2.15 Å and R-factors of 19.5% and 18.3%, respectively.In the R78K variant structure, the high-affinity phosphate group (P1) is missing, consistent with the wild-type structure showing a bidentate interaction between P1 and Arg78, and solution data showing a decrease in P1 affinity in the variant. The structure explains why the mutation affects P1 and pyrophosphate binding much more than would be expected by the loss of one hydrogen bond: Lys78 forms an ion-pair with Asp71, precluding an interaction with P1. The R78K variant also provides the first direct evidence that the low-affinity phosphate group (P2) can adopt the structure that we believe is the immediate product of hydrolysis, with one of the P2 oxygen atoms co-ordinated to both activating metal ions (M1 and M2). If so, the water molecule (Wat1) between M1 and M2 in wild-type PPase is, indeed, the attacking nucleophile.The D117E variant structure likewise supports our model of catalysis, as the Glu117 variant carboxylate group is positioned where Wat1 is in the wild-type: the potent Wat1 nucleophile is replaced by a carboxylate co-ordinated to two metal ions. Alternative confirmations of Glu117 may allow Wat1 to be present but at much reduced occupancy, explaining why the pKa of the nucleophile increases by three pH units, even though there is relatively little distortion of the active site.These new structures, together with parallel functional studies measuring catalytic efficiency and ligand (metal ion, PPi and Pi) binding, provide strong evidence against a proposed mechanism in which Wat1 is considered unimportant for hydrolysis. They thus support the notion that PPase shares mechanistic similarity with the “two-metal ion” mechanism of polymerases.

Bifunctional peptide boronate inhibitors of thrombin: crystallographic analysis of inhibition enhanced by linkage to an exosite 1 binding peptide.

The affinity of the hirudin49-64 segment for exosite 1 of thrombin has been used previously to enhance the potency of simple competitive inhibitors [DiMaio, J., Gibbs, B., Munn, D., Lefebvre, J. , Ni, F., Konishi, Y. (1990) J. Biol. Chem. 265, 21698-21703., and Maraganore, J. M., Bourdon, P., Jablonski, J., Ramachandran, K. L., and Fenton, J. W., II (1990) Biochemistry 29, 7095-7087.]. Using a similar approach, we have enhanced the activity of two active site directed thrombin inhibitors by attaching this segment via a novel reverse oriented linker to each of two tripeptide boronate inhibitors. At P1, compound 1 contains an arginine-like, isothiouronium, side chain, while compound 2 contains an uncharged, bromopropyl residue. Inhibition of human alpha-thrombin by compound 1 shows slow, tight-binding competitive kinetics (final Ki of 2.2 pM, k1 of 3.51 x 10(7) M-1 s-1, and k-1 of 1.81 x 10(-)4 s-1). The addition of hirugen peptide (20 microM) competes for exosite 1 binding and restores the k1 and k-1 to that of the analogous tripeptide, 0.29 x 10(7) M-1 s-1 and 0.13 x 10(-)4 s-1, respectively. Compound 1 has enhanced specificity for thrombin over trypsin with KiTry/KiThr of approximately 900 compared to the analogous tripeptide, with KiTry/KiThr of approximately 4. Compound 2 acts as a competitive inhibitor (KiThr of 0.6 nM) and is highly selective with no effect on trypsin. Crystallographic analysis of complexes of human alpha-thrombin with compound 1 (1.8 A) and compound 2 (1.85 A) shows a covalent bond between the boron of the inhibitor and Ser195 (bond lengths B-O of 1.55 and 1.61 A, respectively). The isothiouronium group of compound 1 forms bidentate interactions with Asp189. The P2 and P3 residues of the inhibitors form interactions with the S2 and S3 sites of thrombin similar to other D-Phe-Pro based inhibitors [Bode, W., Turk, D., and Karshikov, A. (1992) Protein Sci. 1, 426-471.]. The linker exits the active site cleft of thrombin forming no interactions, while the binding of Hir49-64 segment to exosite 1 is similar to that previously described for hirudin [Rydel, T. J., Tulinsky, A., and Bode, W. (1991) J. Mol. Biol. 221, 583-601.]. Because of the similarity of binding at each of these sites to that of the analogous peptides added alone, this approach may be used to improve the inhibitory activity of all types of active site directed thrombin inhibitors and may also be applicable to the design of inhibitors of other proteases.

The mechanistic basis for diastereoselectivity in the Matteson rearrangement

The diastereoselective rearrangement of α,α-dichloromethylboronate derivatives of chiral 1,2-diols (Matteson rearrangement) can be understood readily in terms of a bidentate interaction between the catalytic Lewis acid (ZnCl 2) and the substrate, leading to favored transition states such as 4 and 5.

Activation-induced bi-dentate interaction of SHIP and Shc in B lymphocytes.

SHIP is a SH2 domain-containing inositol polyphosphatase that is selectively tyrosine phosphorylated and associated with the adapter protein Shc in B lymphocytes upon co-crosslinking surface immunoglobulin and Fc gamma RIIB1. We previously observed that this stimulation condition is associated with a reduction in the interaction of Grb2 with phosphorylated Shc, an enhanced interaction of Shc with SHIP, and a block in the Ras signaling pathway. We proposed that the SH2 domain of SHIP competes with Grb2 in binding to phospho-Shc, resulting in a block in Ras signaling. To test this model, we examined the mode of SHIP-Shc interaction. Using recombinant Shc and SHIP interaction domains and purified Shc and SHIP phosphopeptides, we show that the interaction is bi-dentate such that the SH2 domain of SHIP recognizes phosphorylated Y317 and doubly-phosphorylated Y239/Y240 of Shc and the Shc PTB domain recognizes phosphorylated NPxpY motifs within SHIP. We observed no role for the Shc SH2 domain in the interaction. These findings are consistent with our earlier model that SHIP and Grb2 compete for binding to phospho-Shc and support the notion that, in addition to the hydrolysis of inositol phosphates and phospholipids, SHIP contributes to anti-proliferative biochemistry by blocking protein-protein interactions.

IR studies of adhesion promoters. Part 2.—Adsorption of an alkyltrimethoxysilane and alkylamino-trimethoxysilane on silica at the solid/liquid interface

IR spectra of (MeO)3SiMe on silica, in two states of hydroxylation immersed in heptane or carbon tetrachloride, and during desorption after removal of solvent, show that hydrogen bonding of (MeO)3SiMe to two or three SiOH groups at low coverages is replaced by 1 : 1 silanol-silane interactions at high coverage. Adjacent surface silanol groups favour a bidentate interaction, in part involving pairs of silanol groups forming H bonds to single OMe groups. The adsorption of (MeO)3SiCH2CH2CH2NH2 favours bi- or tridentate H bonding via OMe groups at low coverages but a single H bond via the NH2 group of each adsorbed molecule at high coverage.

Transition Metal Chemistry of Main Group Hydrazides. 5. Functionalization of Methylhydrazine With Alkyl/Alkoxy Groups and Aryl/Aryloxy-Substituted Phosphorus(V) Oxides and Sulfides. First Examples of Bidentate Interactions of R2P(E)(NMeNH2) (R = OMe, OEt, OPh, Ph: E = S, O) with Pd(II). X-ray Structure of (MeO)2P(S) NMeMH2.cntdot.PdCl2

The reactions of alkoxy-, aryloxy-, and aryl-substituted phosphorus monochlorides (R{sub 2}P(E)Cl: R = OCH{sub 3}, E = S; R = OC{sub 2}H{sub 5}, E = S; R = OC{sub 6}H{sub 5}, E = ); R = C{sub 6}H{sub 5}, E=o) with methyl hydrazine yielded the new monophosphorus hydrazides 1-4 reacted smoothly with PdCl{sub 2} (PhCN){sub 2} at 25{degrees}C to give the new cyclopalladaphosphohydrazides R{sub 2}P(E)MNeNH{sub 2}{center_dot}PdCl{sub 2} (R = OCH{sub 3}, E = S (5); R = OC{sub 2}H{sub 5}, E = S (6); R = OC{sub 6}H{sub 5}, E = O (7); R = C{sub 6}H{sub 5}, E = O (8) in good yields as air-stable crystalline solids. The chemical constitutions of 1-4 and 5-8 were established by complete NMR ({sup 1}H and {sup 31}P) spectroscopic and C, H, N, and Cl analysis data. The structures of 5 was further confirmed by X-ray diffraction study. Crystal data for 5: monoclinic, space group C2/c, with a = 25.029(9) {angstrom}, b = 10.2800(10) {angstrom}, c = 9.167(3) {angstrom}, {beta} = 104.750(10){degrees}, and Z = 8. The structure was solved by direct methods and was refined to R = 0.035.

Dicalcium 1,4,5,8-naphthalenetetracarboxylate pentahydrate

In the title structure, the 1,4,5,8-naphthalenetetra-carboxylate anion possesses 2/m symmetry with the twofold axis coincident with the central C--C bond of the naphthalene rings. The ten atoms comprising the naphthalene core have a mean deviation of 0.033 A from the best least-squares plane describing these atoms, with the carboxyl C atom 0.395 (2) A removed from the plane. The dihedral angle between the carboxylate plane and the least-squares plane of the naphthalene rings is 46.2 (3) degrees. The O--C--O angle of the carboxylate group, 121.13(12) degrees, is smaller than normally expected, presumably due to the bidentate interaction with the Ca ion. The Ca ion is coordinated by eight O atoms: six carboxylate O atoms and two water O atoms. Because the Ca ion resides on a twofold axis there are only four independent Ca--O distances, which are in the range 2.368 (1)-2.681 (1)A. In this structure, the organic anions are separated by Ca ions and water molecules such that there are no short-range organic-organic interactions. One of the water molecules separating the organic anions is not involved in coordination with Ca, and is disordered.

Molecular Recognition of Phosphate Esters: A Balance of Hydrogen Bonding and Proton Transfer Interactions

AbstractThe interaction of different phosphate esters with a series of hydrogen bonding receptors has been studied using UV‐visible and NMR spectroscopies and X‐ray crystallography. Critical for binding is a combination of an acidic proton and the potential for bidentate hydrogen bonding either between charged or uncharged components. Phosphotriesters show no binding to the receptors. Phosphodiesters bind to both bis‐(2, 6–diacylaminopyridine) and mono‐(2, 6–diacylaminopyridine) receptors in chlorocarbon solvent via proton transfer to form the pyridinium phosphate ion pair and bidentate hydrogen bonding between the anion and the cation. Titration experiments as well as Job's analyses show that for cyclic and acyclic bis‐(2, 6–diacylaminopyridine) receptors 2: 1 complexes can be formed. X‐ray crystal structures demonstrate that in the solid state two different binding arrangements are present; either a direct bidentate interaction or intramolecular hydrogen bonding with self‐assembly of an oligomeric structure. Phosphomonoesters bind to mono‐(2, 6–diacylaminopyridines) in a similar way to the diesters, via proton transfer and bidentate hydrogen bonding. In this, as in the diester case, only a single acid‐base interaction is possible and proton transfer is preferred. However, in the interaction of phosphomonoesters with bis‐(2, 6–diacylaminopyridine) derivatives two acid‐base interactions are possible between the two pyridines and two POH groups, and little proton transfer is seen. Strong binding (Ka = 1.0 × 105M−1) occurs via tetrahydrogen bond formation. Thus, there appears to be a balance between the occurrence of proton transfer and the number of hydrogen bonds formed between receptor and substrate.

Theoretical Design of a Bistetrapeptide Derivative of Mitoxantrone Targeted Towards the Double-Stranded Hexanucleotide Sequence d(GGCGCC)2

The hexanucleotide d(GGCGCC)2 is encountered in recurrent fashion within transcriptional activating sequences in retroviruses and protooncogenes. Our first theoretical design of novel oligopeptide derivatives of mitoxantrone, MTX (1), had enabled us to predict derivatives depsiGly-Lys(L) and depsiGly-Gly-Orn(D) to preferentially target the tetrameric core d(CCGG)2. Owing to the crucial importance of hexamer d(GGCGCC)2, we have attempted to extend the realm of our approach by now targeting this specific hexanucleotide. For that purpose, we undertook the design of further oligopeptide derivatives of MTX, in which each arm was identically amidated (rather than esterified as in (1)) by tri- or tetrapeptides of varying sequences and individual residue configurations. The binding affinities of these derivatives to the palindromic sequences d(GGCGCC)2, d(CGCGCG)2, d(GCCGGC)2 and d(CCCGGG)2, were compared by energy-minimization. We report here the results obtained with the most promising derivative, having the sequence Arg(L)-Gly-Val(L)-Glu(L), and displaying a considerable energy preference for d(GGCGCC)2 over the other candidate hexameric sites (referred to as I). In the corresponding complexes, the two arms are in two mutually antiparallel directions in the major groove, and adopt a beta-sheet like arrangement stabilized by two H-bonds involving the carbonyl and amide groups of the Gly residues. Each Arg side chain on a given arm chelates O6 and N7 atoms of G1, G2/G1', G2' with its imino and cis amino hydrogen, and is simultaneously bound through two amino hydrogens in a bidentate interaction with the Glu residue.

Irreversible H2-antagonism of the four isomeric butyl analogues of mifentidine

It has been hypothesized that bidentate hydrogen bonding plays an important role in the interaction of imidazolylphenylformamidines with the H2-receptor. The present study, in which the degree of pseudo-irreversible H2-antagonism of the four isomeric butyl substituted mifentidine analogues was determined on the spontaneously beating right atrium of the male guinea-pig, lends further support to this hypothesis. In solution the EE/EZ ratio is different for the four isomeric butylated mifentidine analogues. The rank order of the percentage of E,E conformation, which favors a bidentate interaction, of the formamidine moiety parallels the rank order of pseudo-irreversible H2-antagonism.

A theoretical investigation of the base sequence preferences of monointercalating polymethylene carboxamide derivatives 9-amlnoacndine

Theoretical computations are performed of the comparative binding affinities of five polymethylene carboxamide derivatives of 9-aminoacridine to a series of double-stranded hexanucleotides. The purpose of this investigation is to ascertain whether minor groove recognition of a guanine base adjacent to the intercalation site can occur, and be preferentially stabilized, for a given length of the polymethylene side chain, encompassing from n = 2 up to n = 6 methylene groups. For that purpose, several representative sequences were investigated, in which intercalation of the 9-aminoacridine chromophore occurred at a central d(CpG) or d(TpA) step. Investigated were the self-complementary sequences d(CGCGCG)2, d(GCCGGC)2, d(TATATA)2 and d(ATTAAT)2, as well as the 'mixed' sequences d(ACTAAT) .d(ATTAGT) and d(TGTATA). d(TATACA). For n = 3 up to n = 6, such a recognition was enabled only when the guanine base was located downstream of the intercalation site, i.e. with steps d(CGG) and d(TAG). It occurred by means of a bidentate interaction involving, on the one hand, H(N2) and N3 of the base, and, on the other hand, the carbonyl oxygen and the cis amino hydrogen of the terminal formamide moiety of the ligand. Because of the flexibility of the side chain, however, alternative binding modes were also found to occur competitively, involving backbone-only interactions of the side chain. On the basis of the present computations, upon binding to the sequence d(GCCGGC)2, an optimal value of n = 5 could be derived, with the corresponding acridine derivative eliciting both a significant prevalence of the bidentate over backbone only binding mode, and the most favourable energy balance within the investigated series. This privileged value of n = 5 is fully consistent with the experimental results of Markovits et al. and Gaugain et al. The very flexibility of the side chain, however, hampered any preferential recognition of a triplet sequence with a downstream guanine, such as d(CGG) or d(TAG), to be elicited over sequences such as d(TAA), d(TAT) or d(TAC).

Infrared spectral studies of various metal polyacrylates

A new process for the production of high surface area, high reactivity ceramic oxide powders involves the bonding of metal cations to polymeric polyacrylate chains. This process results in the formation of a gelatinous metal polyacrylate precipitate which can be easily removed from the mother liquor, and then calcined to form a high density ceramic oxide. Using FTIR spectroscopy, the nature of the structural arrangements has been studied for metal complexes in the yttrium, lanthanum, aluminum, cerium, copper, and iron polyacrylates. Interpretation of the infrared spectra indicates that two types of metal complex formation occur in these precipitates, involving bidentate or bridging interactions. The type that is observed for a particular metal ion is dependent on its metal ion size.

INTERACTION OF MONOSACCHARIDES AND RELATED COMPOUNDS WIT OXOCATIONS OF MO(VI), W(VI) AND U(VI)STUDIED BY NMR SPECTROSCOPY

Abstract Proton, 13C and 31P nuclear magnetic resonance spectroscopy has been used to study the complexation of M(VI), W(VI) and U(VI) oxocations with various aldoses, cyclic polyols and ribose-5-phosphate in aqueous solution. The aldoses D-mannose, D-lyxose and D-ribose from tridentate complexes with Mo(VI) and W(VI) at pH ≃ 5, via the 1,2,3-hydroxyl groups, which are cis to each other in these sugars. Other aldoe, like D-arabinose, D-glucos, D-xylose and D-galactose from weaker bidentate complexs with those ions because they can onl use the 1 and 3-cis hydroxyl groups in metal binding. These bidentate interactions also take place in the binding of U(VI) to D-ribose, at pH ≃ 110. However, sugars having 1,3,5-hydroxyl groups in the cis position do not from stable chelates with these oxocations, possibly due to steric crowding. In the case of ribose-5-phosphate, the phosphate group is the exclusive binding site for the three oxocations. except for U(VI) at ver basic pH(pH > 10), where the hdroxyl groups al...

A quantitative approach to host–guest interactions for matrix-isolated alkali-metal salts of hexafluoroanions and perchlorates

From matrix-isolation i.r. studies it is demonstrated that heavier alkali-metal salts of a number of hexafluoroanions can be vaporised as molecular species. In all cases there is some decomposition and this is particularly serious for the non-transition elements. The i.r. spectrum of CsNbF6 in a range of matrix gases is reported in the Nb–F stretching region. It is found that for matrices where the host–guest interaction is expected to be weak (Ne, Ar) a characteristic doubling of ν3 of the NbF6– ion is observed. This is interpreted as due to the presence of a tridentate (facial) interaction between the caesium ion and the NbF6– anion. For matrices where the host-guest interaction is expected to be stronger (CO, N2) a characteristic triplet is observed and this is interpreted as due to a bidentate (edge) interaction between the caesium ion and the NbF6– ion. In an attempt to calibrate the host–guest interaction CsClO4 is studied in a range of matrix gases. The separation between the ‘terminal’ stretching frequency and the ‘bridge’ stretching frequency is taken as a measure of the interaction between the CsClO4 and the matrix. This leads to the following sequence in order of decreasing frequency separation: Ne > Ar > 02≈ F2 > Kr > Xe > N2 > CO. (Neon showing the greatest separation is assumed to have the smallest host-guest interaction.) When the above frequency separations for CsClO4 are plotted against those for CsNbF6 in the same matrix gases there is a close correlation between the two. Further, those matrices in which a doublet behaviour is observed for CsNbF6are precisely the ones which interact weakly in terms of the above sequence (Ne, Ar, O2, F2, Kr); a triplet is found for matrices showing a stronger interaction(CO, N2) For xenon (and to a lesser extent krypton) both doublet and triplet forms are present. The spectrum of CsNbF6 in a 1:1 mixture of argon and nitrogen is strikingly similar to that in xenon.

A specific 2,4‐disubstituted‐adamantane interaction with plasma‐grown aluminium oxide. An inelastic‐electron‐tunnelling spectroscopy study

AbstractThe interaction of several mono‐ and disubstituted adamantanes with plasma‐grown aluminium oxide has been studied using inelastic‐electron‐tunnelling (IET) spectroscopy. The IET spectra evidence the chemisorption of 2,4‐adamantanedione (1) onto the aluminium oxide surface as the carboxylate anion of bicyclic acid ketone 2, which is formed by ring opening of the β‐diketone. In the case of 4‐hydroxy‐2‐adamantanone (3), no ring opening to the corresponding bicyclic acid (4) is observed. 3 is chemisorbed as aluminium alkoxide through condensation. Stabilization by additional hydrogen bonding between the aluminium oxide and the keto group seems to be required since 1‐adamantanol, 2‐adamantanol and 2‐adamantanone do not adsorb onto the aluminium oxide. Even 5‐hydroxy‐2‐adamantanone is not bonded to the surface, indicating the necessity of a specific 2,4‐disubstituted adamantane bidentate interaction with aluminium oxide.

Patents on videodisc. A Future system almost with us

Combining functional organic self-assembled monolayers (SAMs) with conventional semiconductor materials is a key step in the development of integrated electronics-based devices. T-BAG (Tethering by Aggregation and Growth) has been shown to be a simple and reliable method to grow SAMs of alkylphosphonates on oxide surfaces. However, distinguishing SAMs from ultra-thin multilayers is a challenge for most conventional surface characterization techniques.Self-assembled films of octadecylphosphonic acid (ODPA) were deposited on oxide-covered silicon coupons, converted to the corresponding phosphonates, and characterized by high resolution angularly resolved X-ray photoelectron spectroscopy (XPS). It was our goal to distinguish among different bonding configurations for phosphorous in the phosphonate head groups, namely, mono-dentate, bi-dentate or tri-dentate interactions with the oxide surface, as well as to assess quantitatively the near-surface layer composition.We also present an innovative method that allows us to distinguish between monolayer and multilayer films of ODPA on silicon oxide surfaces. This method is based on differential surface charging effects in XPS. It was found that variation in the ODPA film thickness causes differential responses of various spectral characteristics to an electrical bias applied to the sample during XPS measurements. Both positive and negative applied biases were found to affect the carbon core-level (C1s) line-shape and intensity in the case of the multilayer ODPA film, whereas line-shapes and intensities of all XPS lines measured for the monolayer film were unaffected by the application of a dc bias in the ±30 V range.